Thursday, 27 September 2012

Over the past couple of weeks I’ve been doing a lot of work with WCF to do with the messages being sent between client and server and securely signing them. Signing the message isn’t the subject of this post however developing the following technique to see the message before it’s sent did lead me onto the solution for debugging messages being sent between client and server.

This post is to show how you can intercept the message, update it once its been serialized into xml (or just look at the xml) but before it’s been sent to the server. The basis of this all down the the IClientMessageInspector and adding this to your client calling code.

Let’s take a look at the message inspector and then I’ll talk through the additional classes which go with the inspector and then finally I’ll show you how to use the message inspector with a WCF client proxy generated class; in both code and through configuration.

Above is the generated method signatures of which the IClientMessageInspector expects to be implemented. The naming of the methods describes exactly the point in which they are called; BeforeSendRequest is as the request is sent to the server, AfterReceiveReply is as the response is returned. On the way out this is executed after the message has been created from the strongly typed objects and on the way in it executes before any serialization is performed if using strongly typed proxy and class definitions generated from a WSDL.

Inside each of the methods you can call the following code to allow inspection of the message.

private Message Intercept(Message message) { // read the message into an XmlDocument as then you can work with the contents // Message is a forward reading class only so once read that's it. MemoryStream ms = new MemoryStream(); XmlWriter writer = XmlWriter.Create(ms); message.WriteMessage(writer); writer.Flush(); ms.Position = 0; XmlDocument xmlDoc = new XmlDocument(); xmlDoc.PreserveWhitespace = true; xmlDoc.Load(ms);

// read the contents of the message here and update as required; eg sign the message

As you can see a number of extension hook points are available, but for this post we’ll concentrate on the “ApplyClientBehavior” method. In this method it gives you access to the MessageInspectors collection on the ClientRuntime which is a SynchronizedCollection on which any IClientMessageInspector implemented class instances can be added to.

This is it for the behavior definition. Lets see how we use it with a WCF client proxy class.

How do we use the IClientMessageInspector?

There are two ways in which the inspector can be used with a client proxy class. It can either be added in via code or through configuration. There are pros and cons for both routes. If done through code it will always be added, however a con is it will always be added. If however it is done through configuration it can be enabled/disabled without recompiling the code. This can be especially handy if the functionality is only for debugging and you don’t want it to be used during Production or it’s used to turn on/off certain functionality which is only applicable under certain circumstances.

Let’s take a look at using the message inspector first with code and then through configuration.

Using the IClientMessageInspector in code

Through code (example code can be found on GitHub) you add it to the Endpoint Behavior collection directly. This can be done either straight after the proxy definition or at any point before any method is actually executed.

As you can see from the above it is instantiated calling a default constructor. At this point you can pass in constructor parameters however this will cause you issues if you want to move it to be bound in configuration later.

And that’s it. Straight forward; simple.

Using the IClientMessageInspector through configuration

Adding the behavior through configuration takes a bit more work but as stated earlier being able to attach the functionality purely through configuration without changing code is worth the extra effort. To attach through configuration we need to define a new BehaviorExtensionElement which describes our new behavior.

This is all in the system.serviceModel node in your web/app config file. The important parts are highlighted in bold.

First off you have to define a behavior extension pointing at your newly created behavior element class. This is a reflection string so the fully qualified type name needs to be followed by the name of the assembly that contains it.

Secondly you create an endpoint behavior which now uses the newly created extension. At this point the intellisense in Visual Studio will complain however it’s fine.

Third and finally you specify the newly created endpoint behavior as the behaviorConfiguration for your client end point.

Conclusion

Message inspectors are a very powerful tool when working with WCF and integration services. They can be used for debugging purposes as shown or for performing other actions on the message before it gets sent or on its return such as securely signing the message with a certificate.

The demo code I’ve used for this post can be found on Github; but remember it comes with a “Works on my machine” seal so use at own risk.

Sunday, 23 September 2012

John Papa published a very good course on Pluralsight the other day about how to create a Single Page Application (SPA) and due to the popularity of the course Pluralsight opened it up for a short time only for free (thanks!). This allowed me to see exactly the type of quality I would receive when my training budget at work comes through soon (fingers crossed for October).

After watching some of the videos it was really interesting but I wasn’t quite getting how it all fitted together in the solution so was very pleased to find that the free sign up included being able to download the course material including the final solution. After downloading the zip file, expanding the contents and locating the .sln file I double clicked it and waited for Visual Studio 2010 to fire it up.

On Visual Studio 2010 opening the solution I was presented with a very sad looking solution explorer.

This is due to the fact that the course was written in Visual Studio 2012 and hence .net 4.5 was used for the projects. This got me thinking that it shouldn’t cause a problem as all the technologies which were being used are also available for .net 4 so I got about trying to get it to work.

Step 1; getting the projects to load

This in itself wasn’t that tricky. Firing up the .csproj files in notepad and locating the TargetFrameworkVersion I changed it to “v4.0”, saved and repeated it for all of the projects in the solution.

<TargetFrameworkVersion>v4.5</TargetFrameworkVersion>

To

<TargetFrameworkVersion>v4.0</TargetFrameworkVersion>

Once all the projects had been updated I reopened the solution in Visual Studio 2010 and got a prompt about configuring IISExpress. CodeCamper is configured to use IISExpress however if you don’t have it installed you will need to install it or configure the solution to work on a local IIS instance.

On clicking “Yes” Visual Studio attempted to load up the projects and Resharper did it’s usual solution scan and I was presented with a much happier looking solution explorer.

Step2; Lets try and build

On building the solution I got the following warnings however it did build.

warning CS1684: Reference to type 'System.Data.Spatial.DbGeometry' claims it is defined in 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\System.Data.Entity.dll', but it could not be found warning CS1684: Reference to type 'System.Data.Spatial.DbGeography' claims it is defined in 'c:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0\System.Data.Entity.dll', but it could not be found

After a “successful” build I fired up the IISExpress site and went to start browsing the site to start seeing how it fitted together. However this was not the case and I got the following error.

Step3; changing 4.5 to 4

The changing of required framework version had not finished at the csproj level so I went through the web.config of the asp.net mvc project and changed the targetFramework attribute to “4.0”.

I also removed targetframework=4.5 from the httpruntime element below. Removed the machine key below that and hit refresh.

By now I was pretty sure that dependencies and reference errors are likely to be due to the framework version. With this I did a little Google and found that the version number had been bumped up to 4 for System.Net.Http in .net 4.5 however for .net 4.0 this needs to continue to reference version 2. With this in mine I updated the web.config from:

At this point I decided I would ignore the AntiXss encoder reference for now and come back to it later. I’m not going to publish the site anywhere so not worried about cross site scripting. However if you are going to put a site up into the wild then you will need to stop this kind of attack. Discussion for this is out of scope for this post.

I hit refresh and was presented with the Code Camper blue screen as below.

However no data.

step 4; getting data

At this point I thought I’m pretty close and pretty sure this will have something to do with the connection string. So after checking the connection strings configured in the web.config and noticing which one was currently active I checked to make sure the CodeCamper.sdf was present and ran.

Nothing; so changed the CodeCamperDatabaseInitializer below to always drop and recreate the DB to make sure the DB was fresh with the seeded data (remember to remove this and put it back to one of the other options otherwise it will delete everything all the time).

Nothing. At this point I decided to remove the sdf file and update the connection string to use to be the SQLExpress one. I knew I had that installed and running so would be perfectly fine for study purposes.

Time to try running it again to see which error would occur next. The next error was inside the NInject Dependency Scope implementation, in the NinjectDependencyScope.GetService(Type serviceType) method …

This was due to a version miss match of Ninject; uninstalling the Ninject nuget package and reinstalling it to get the correct version down seemed to resolve this.

Another rebuild and run. This time the EntityFramework was not happy with the current build. After the last issue with Ninject I thought I’d try the same routine so I uninstalled the EntityFramework nuget package and reinstalled it. It seemed to be originally wanting .net 4.5 but it’s happy with 4. This needed to be done in both the CodeCamper.Data and CodeCamper.Web projects.

At this point I hit f5 and crossed my fingers. I was greeted with a screen full of green friendly messages about getting data from the asp.net web api and a smiling photo of the mighty ScottGu; finally I’d got it working!

Conclusion

There is one out standing issue which was not resolved and that is around the AntiXss functionality but the rest seems to work as expected.

Thanks again to John Papa and Pluralsight for creating and publishing this course and I can’t wait to get my full subscription to start enjoying the other courses.